The invention relates to lubricant fittings adapted to be connected to a valve body, and in particular, to a lubricant fitting of the back seat type.
Heretofore, in high pressure situations (e.g. 20,000 psi), the use of lubricant fittings of the back seat type have proven satisfactory for injecting lubricant material into the interior of the valve body. These lubricant fittings have also provided an adequate seal when the pressure in the interior of the valve body is above a predetermined level (e.g. 50 psi). U.S. Pat. No. 3,605,948 issued to Wynn on Sept. 20, 1971, is exemplary of these earlier lubricant fittings which are adapted to be connected to a valve body. However, these lubricant fittings do not have satisfactory sealing characteristics when the pressure in the interior of the valve body is lower than approximately 50 psi. The inability of these lubricant fittings to seal at low pressures is of great concern, especially in critical service applications where hydrogen sulfide is present. Thus, it would be highly desirable to provide an improved lubricant fitting that performs effectively by providing adequate sealing characteristics at low pressures (e.g. 50 psi or less) as well as at high pressures (e.g. 20,000 psi). It would also be highly desirable if this improved lubricant fitting could be mechanically sealed to insure that regardless of the pressure in the interior of the valve body the lubricant fitting will adequately seal.